izarc file asocciations

Hi I want to deploy a freeware unzip program like 7zip or (preferred) izarc on my W2K systems.
I have no problem finding the command line switches for a silent install. However, after
the installation there is still no file association for .zip, .lzh, etc for the program.
Since this is an unattended install, I would like to know how to get this done without
opening the program and check the .zip, .lzh, etc boxes in the options screen by hand.